Simulation and experimental investigation of performance and emissions of a turbocharged lean-burn natural gas engine considering thermal boundary layer

Emission characteristics of pure natural gas is fairly known, however moreexperimental investigation of natural gas combustion is necessary. in this research, emissionand performance of a turbocharged natural gas si engine are investigated experimentallyat wot and lean burn conditions. a computer code is also developed in matlabenvironment for predicting engine performance and no emission and the results arevalidated with experimental data. thermal boundary layer, as a novel approach, isconsidered in the simulation and a better agreement of predicted mass fraction burnedwas achieved at end part of combustion process when compared with experimental results.experimental results have revealed that turbocharger match at mid engine speed, wastegateopening and increase of friction losses at high engine speed resulted in better torqueback-up. boost pressure, controlled by compressor outlet pressure, remained nearlyconstant at speeds higher than 1450 rpm. no emission reduced with engine speed increasedue to shorter time that burned gases remain at high temperatures, although they havehigher temperature at higher speeds. it however increased with the increase of excess airratio until it reached to its peak value at about 1.1 from stoichiometric mixture and thendecreased, while it decreased substantially with increase of spark timing retard. brakespecic uhc and co2 emissions were min at mid speed range and wot.